what does port height effect?

[ncc74656]

I have read that the basic idea is you multiply the total cubic volume of the box by 12-16 and then divide that by the width of the port to get the range of port height. is this correct?

if that is correct then my question is if a port is 30" wide in a 8 cubic foot box then how does a 3.2" height port differ from a 4.26"? will the two sound different or does it only effect the port noise?

[noph33rracing]

30x3.2=96 sq inches of port

30x4.26=127.8 sq inches of port

going off the 12-16sq inches of port per cube rule you want between 96sq inches and 128 sq inches of port so either work. you just need to figure out what you want to tune to and see which one will work. tuning depends on how deep into the box the port goes.

either could work.

sometimes people will use more port if they are running less power

vs

you could also run a smaller port if your throwing a lot of power at your subs

[ncc74656]

i had thought that the more power the larger the port you should have? im not sure what my tuning is going to be, my idea is to build the box a smig larger than needed and start at 30hz with no bend in the port and take it down from a 19" port to a 40" port up to 38hz and test out the frequency sweep. adding extra side bracing to reduce cubic footage as i go.

[Joe X]

For a rectangular port keep area ratio below 9:1 for example H=8 W=2 , 8/2=4 which is less than 9 so the ratio is acceptable.

The 12-16 rule is just statistics, most boxes calculated by other methods will fall within that range but then some others won't.

.

[CleanSierra]

As Joe said, the 12-16 is a generic guideline. Tuning frequency, xmax and cone area are what really determine how much port to give x sub in y enclosure. For example, a HIGH xmax sub with a bunch of cone area will need more port per square foot than a smaller sub with NOT a lot of xmax(linear excursion). If we kept the same port aspect ratio with both enclosures, one or both setups would not be optimal. I.think the main thing in mobile installs is avoiding port noise more than anything. Since a wave doesn't typically FULLY develop(especially the ultra low frequencies) as long as you have ENOUGH port, you'll never notice noise. Same enclosure in a big 20X20 room? You might notice some pretty significant noise.